1. Field of the Invention
The present invention relates generally to fluid filled vibration damping mounts such as used to support power units, cabs and/or body structures on vehicle chassis and the like and more specifically to such a type mount which features improved rigidity against axially acting and the like type forces.
2. Description of Prior Art
JP-A-63-318339 discloses a so called bush type of vibration damping mount which is used to support engines, cabs and/or body structures on vehicle chassis wherein two coaxial essentially horizontally (parallel) arranged inner and outer structural members are supportingly connected by way of an elastomeric body.
This arrangement includes an expansion chamber which is defined between the inner member and the elastomeric body and a working chamber which is defined between the elastomeric body and the outer member. The working and expansion chambers are fluidly interconnected by an orifice passage in a manner which enables vibration which is applied to the bush to be attenuated by pumping a working fluid back and forth between the two chambers.
This particular mount is such that the elastomeric body is vulcanized to the inner member along with a rigid insert member. The latter mentioned insert is arranged to have an orifice defining recess which communicates at its both ends with a fluid chamber defining recess formed in the elastomeric body. This combination is inserted into a cylindrical outer member which has an elastomeric layer partially vulcanized to a predetermined portion of the inner periphery thereof.
In order to ensure that the orifice passage and the fluid chamber are completely filled with working fluid and all air is excluded, it has been discovered that the assembly of the inner and outer members must be made while the components are totally immersed in the working fluid. The outer member is then subject to external compression in a manner to fix the two parts together into a single unit.
However, with this arrangement a problem has been encountered in that an air chamber which is defined between a portion of the elastomeric layer which is not vulcanized to the outer member and the outer member itself, is communicated with the ambient atmosphere by way of only a single relatively small diameter opening.
During the immersed assembly, the above mentioned air chamber becomes filled with working fluid which must be drained therefrom. However, due to the provision of the single small opening, the drainage of the same requires a long time and troublesome operations wherein each unit must be tilted and turned through various angles to induce draining. In fact total removal is impossible to achieve.
To overcome this, it has been proposed to provide a relatively large window type opening which opens into the air chamber. This has successfully overcome the draining problem and enable the ready cleaning of the air chamber but has in turned encountered a drawback in that, when the bush is forced fitted into a suitable section of a mounting bracket, a relatively large force needs to be applied to one end of the device in order to force it all the way home. This force acts along the longitudinal axis of the outer cylindrical member. However, the provision of the enlarged window reduces the structural strength of the outer member to the degree that during the force fitting process, buckling or otherwise undesired distortion of the outer member tends to occur.
Needless to say, such distortion can require that the unit be removed from the bracket and replaced with a new one. This of course leads to highly undesired increases in lost time and production costs.